1. Field of the Invention
The present invention relates to a communication management apparatus and a communication management method that manage sessions established between users for communication, and, more particularly to a communication management apparatus and a communication management method that can resume service quickly, while securely recovering a session.
2. Description of the Related Art
Conventionally, in a line-switching communication system in which communication is started after a communication line is established between a caller and a callee, various methods have been studied for recovering an established line of a call even in the event of failure. For example, a process is described in Japanese Patent Application Laid-Open No. H7-123451 in which data required for call recovery is stored in a memory, and is referred to for restoring the call.
The conventional process described above has been studied for session recovery in a communication control protocol such as session initiation protocol (SIP). A simple description of session recovery in SIP is given below with reference to FIG. 8.
In SIP, a SIP server controls sessions established one-to-one between a plurality of callers and a plurality of callees. FIG. 8 is a sequence diagram of session recovery performed when failure occurs after establishment of a session between a caller and a callee. As shown in FIG. 8, when establishing a session, the caller sends a session initiation request to the SIP server (step S1) and the SIP server forwards the session initiation request to the callee (step S2).
Upon receiving the session initiation request, the callee sends a session initiation response to the SIP server (step S3) and the SIP server forwards the session initiation response to the caller (step S4). Upon receiving the session initiation response, the caller sends a reception acknowledgment response (ACK) to the SIP server (step S5) and the SIP server forwards the ACK to the callee (step S6), establishing a session between the caller and the callee. The SIP server has a memory in which are stored data concerning session control such as session state management (hereinafter, “session control data”) and data concerning resources used in the established session (hereinafter, “call process resource data”).
The caller and the callee communicate using the established session. However, if any trouble is detected because of failure of the SIP server, etc. (step S7), the SIP server performs an initial setting for restoring its function (step S8) as well as creates the call process resource data once again from the session control data stored in the memory (step S9), and recovers the session, which has been in a stable communication state.
After the session recovery, the caller sends a session update request to the SIP server at regular intervals (step S10), and the SIP server forwards the session update request to the callee (step S11).
Upon receiving the session update request, the callee sends a session update response to the SIP server (step S12) and the SIP server forwards the session update response to the caller (step S13). Upon receiving the session update response, the caller sends an ACK to the SIP server (step S14), and the SIP server forwards the ACK to the callee (step S15), confirming that the session between the caller and the callee is continuing.
However, as the SIP server performs the initial setting and creates the call process resource data during session recovery simultaneously, the restoration of the SIP server is delayed. In other words, when failure occurs, the SIP server performs initial setting as well as session recovery of the already established session based on the session control data stored in the memory. However, this sequence of processes takes a relatively long time, and it takes a long time until the SIP server is restored. The SIP server is unable to receive a new session initiation request in the meantime, resulting in a delay in the resumption of service.